There are known to exist many designs and methods for implanting implantable articles, such as bone prostheses. Such bone prostheses include components of artificial joints, such as elbows, hips, knees and shoulders. An important consideration in the design and implanting of virtually any implantable bone prosthesis is that the bone have adequate fixation when implanted within the body.
Earlier designs of implantable articles relied upon the use of cement, such as polymethylmethacrylate (PMMA) to anchor the implant. The use of such implants can have some advantages, such as providing a fixation that does not develop free play or does not lead to erosion of joining faces postoperatively. However, the current trend is to use the cements to a lesser extent because of their tendency to lose adhesive properties over time and the possibility that cement contributes to wear debris within a joint.
Recently, implantable bone prostheses have been designed such that they encourage the growth of hard bone tissue around the implant. Such implants are often implanted without cement and the bone grows around surface irregularities, for example, porous structures on the implant.
One such implantable prosthesis is a shoulder prosthesis. During the lifetime of a patient, it may be necessary to replace the natural humeral head and associated glenoid cavity with a prosthesis. Such a shoulder replacement procedure may be necessary to be performed on a patient as a result of, for example, disease or trauma, for example, disease from osteoarthritis or rheumatoid arthritis.
Most shoulder replacement surgeries today involve the implantation of a total shoulder prosthesis. In a total shoulder replacement procedure, a humeral component having a head portion is utilized to replace the natural head portion of the upper arm bone or humerus. The humeral component typically has an elongated intramedullary stem which is utilized to secure the humeral component to the patient's humerus. In such a total shoulder replacement procedure, the natural glenoid surface of the scapula is restructured or otherwise replaced with a glenoid component that provides a bearing surface for the head portion of the humeral component.
With the average age of patients requiring shoulder arthroplasty decreasing, orthopaedic implant manufacturers are developing “bone-sparing” implants for the initial treatment of degenerative arthritis. While bone-sparing implants for the treatment of hip and knee arthroplasty are becoming quite common, bone-sparing shoulder arthroplasty techniques and prostheses are also being developed.
Shoulder surface replacement prostheses are being developed to replace the articulating surface of the proximal humerus with a minimal bone resection and minimal disruption of the metaphysis and the diaphysis. Current designs use a semi-spherical articular dome with a small stem for rotational stability. The under surface of the articular head is also semi-spherical and meets with a spherically machined humeral head.
Typically, however, arthritis of the gleno-humeral joint causes flattening of the humeral head with a large medial osteophyte. The flat humeral head can cause voids in the bone under the prosthesis resulting in limited contact between the prosthesis and the resected bone and may limit the load transfer capability between the prosthesis and the humerus.
Referring now to FIG. 2, a healthy long bone or, in the form of, for example, a humerus 1 is shown. The humerus 1 includes a head 2 on the proximal end of the humerus 1. The head 2 of a healthy humerus has a arcuate outer periphery. The arcuate outer periphery is generally hemispherical and meets with a concave glenoid cavity 3.
Referring now to FIG. 3, a diseased humerus 4 is shown. The diseased humerus 4 includes a head 5. The head 5 is flattened as shown in FIG. 3. The humerus 4 also has developed a large medial osteophyte 7.
Referring now to FIG. 4, a prior art prosthesis 8 is shown in position on the head 5 of diseased humerus 4. The head 5 includes a flattened humeral head area or bony defect 9, which leads to a void 6 between the prosthesis 8 and the bony defect 9.
When preparing a humeral head for a bone sparing or conservative shoulder arthroplasty, the semi-spherical humeral head is prepared by, for example, a grater type hollow hemispherical grater-type reamer. Such reamers are available from, for example, Othy, Inc., 460 West 350 North, Warsaw, Ind. 46580.
Additional steps to prepare the humeral head to receive a conservative or bone sparing humeral prosthesis may be required. For example, the bone sparing or conservative humeral prosthesis may include a stem for anchoring the prosthesis into the humerus.
The humeral head needs to be prepared to receive the stem. Typically, a drill and/or a reamer may be required to prepare the prosthesis to receive the stem. Such drills and reamers add time to the surgical procedure as well as represent a problem with the reamer having an orientation off center or skewed with respect to the hemispherical portion of the prepared humerus.
Current resurfacing instrumentation, therefore, addresses bone preparation techniques separately or sequentially. This type of procedure increases time, cost and mistakes. Operating room time is increased because the surgeon and the operating room personnel are handling more instrumentation. Cost is increased because more instruments need to be manufactured and processed. More mistakes can be made because more instruments are handled and consequently the greater is the chance of dropping or making the wrong instrument selection.